You havent really told us anything else about the machine at fault here.
It could be any number of things, my bet is on a flakey motherboard or at least an improperly configured one.
But since you havent told us what motherboard you have, how old it is etc I cant help much.
If you could give us a more detailed spec of your machine that would be Bonza
Oh and if you could mention if there are any onboard components that would be a help too
EDIT: Let me be the first to say Welcome to NTHW
